Battery fault tolerant architecture for cell failure modes parallel bypass circuit

ABSTRACT

A by-pass circuit for a battery system that disconnects parallel connected cells or modules from a battery circuit or controls the current through the parallel connected cells or modules. If a cell has failed or is potentially failing in the system, then the by-pass circuit can disconnect the cell or module from other cells or modules electrically coupled in parallel. If a cell or module has a lower capability than another cell or module, then the by-pass circuit can control the current to the cell or module to maximize the performance of the system and prevent the system from creating a walk-home condition.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to a controllable by-pass circuit forparallel connected battery modules or cells and, more particularly, to acontrol circuit that is able to by-pass connected battery cells ormodules that are part of a larger battery system and control thedischarge and charge current.

2. Discussion of the Related Art

Electric vehicles are becoming more and more prevalent. These vehiclesinclude hybrid vehicles, such as the extended range electric vehicles(EREV) that combine a battery and a main power source, such as aninternal combustion engine, fuel cell systems, etc., and electric onlyvehicles, such as the battery electric vehicles (BEV). All of thesetypes of electric vehicles employ a high voltage battery that includes anumber of battery cells. These batteries can be different battery types,such as lithium ion, nickel metal hydride, lead acid, etc. A typicalhigh voltage battery system for an electric vehicle may include a largenumber of battery cells or modules to meet the vehicle power and energyrequirements. The battery system can include individual battery moduleswhere each battery module may include a certain number of battery cells,such as twelve cells. The individual battery cells may be electricallycoupled in series, or a series of cells may be electrically coupled inparallel, where a number of cells in the module are connected in seriesand each module is electrically coupled to the other modules inparallel. Different vehicle designs include different battery designsthat employ various trade-offs and advantages for a particularapplication.

A battery cell in a battery may fail or may otherwise be limited inperformance for a number of reasons, such as an internal short, loss ofcapacity, high resistance, high temperature, etc. A vehicle battery packtypically includes a variety of sensors and other diagnostic devicesthat can determine if the battery performance is limited, is failing ormay fail in the near future. Because the battery cells may beelectrically coupled in series, failure of one cell in the series mayprevent use of other cells in the series and may result in vehicleshut-down. Therefore, the battery can be disconnected from the circuitbefore a major battery failure has occurred and warning lights can beprovided indicating such a failure.

Depending on the battery type, such a failure may result in a walk-homecondition where the vehicle needs to be towed and cannot be driven. Itwould be desirable to provide a circuit where individual cells of abattery can be switched out of the circuit so that the walk-homecondition and other scenarios may be avoided.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, a by-passcircuit is disclosed for a battery system made up of cells or modulesthat disconnects a cell or module from the circuit or controls thecurrent to and from the cells or modules. If a cell or module hasfailed, or is potentially failing, in the system, then the by-passcircuit can disconnect the cell or module from other cell(s) ormodule(s) electrically coupled in parallel. If a cell or module haslimited performance, then the by-pass circuit can regulate the currentto or from the cell or module to prevent its failure or to slow itsfailure rate.

Additional features of the present invention will become apparent fromthe following description and appended claims, taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a vehicle electrical system;

FIG. 2 is a schematic diagram of a plurality of cells in a vehiclebattery including by-pass circuits;

FIG. 3 is a schematic diagram of a battery by-pass circuit;

FIG. 4 is a schematic diagram of parallel connected battery cells for avehicle battery; and

FIG. 5 is a schematic diagram of a paralleling interface module.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the invention directed toa by-pass circuit for removing a cell or module that is connected inparallel with other cells or modules is merely exemplary in nature, andis in no way intended to limit the invention or its applications oruses.

FIG. 1 is a block diagram of a vehicle system 10 including a highvoltage battery 12. The high voltage battery 12 includes a plurality ofbattery modules 14, each including a plurality of battery cellselectrically coupled in series. In one non-limiting example, the battery12 may include eight of the modules 14, where each of the modules 14 mayinclude twelve cells for a total of ninety-six cells. The total voltagemay be in the 350-400 volt range. The battery 12 is electrically coupledto a high voltage bus represented by lines 16 and 18. In thisnon-limiting design, the vehicle system 10 is part of a hybrid vehiclethat includes a main power source 20, such as an internal combustionengine, fuel cell system, etc. The power source 20 is also electricallycoupled to the high voltage bus lines 16 and 18. The battery 12 and thepower source 20 provide power to the bus lines 16 and 18 in any suitablecontrolled configuration for a particular application, where the battery12 and the power source 20 are matched to the bus lines 16 and 18.Vehicle loads 22 are electrically coupled to the bus lines 16 and 18,and represent any vehicle load that receives power from the vehiclepower systems, namely the battery 12 and the power source 20, such asthe vehicle propulsion system, electric motors, auxiliary loads, etc.Suitable electrical components would be provided to step down thevoltage for those loads that are low voltage loads.

FIG. 2 is a schematic diagram of a battery circuit 30, which can be thecircuit within one of the modules 14, for example. The battery circuit30 includes a battery cell by-pass circuit 32 in association with eachbattery cell 34 in the circuit 30, where the battery cells 34 areelectrically coupled in series. Each by-pass circuit 32 includes a firstswitch 36 electrically coupled in series with the battery cell 34 and asecond switch 38 electrically coupled in parallel with the battery cell34 in a by-pass line 40. The switches 36 and 38 can be any switchsuitable for the purposes described herein, such as solid-stateswitches, relays, mechanical disconnects, etc. Examples of mechanicaldisconnects include back plane and bus-bar designs. Determining whattype of switch to use considers the particular battery design, size andweight considerations, cost considerations, parasitic lossconsiderations, etc. A controller 42 controls the position of theswitches 36 and 38 in each by-pass circuit 32 consistent with thediscussion herein. In this non-limiting embodiment, the controller 42receives temperature signals from temperature sensors 44 in the circuit30.

During normal operation, the switch 36 is closed and the switch 38 isopen so that current travels through the cell 34. If a cell failuremode, or a potential cell failure mode, is detected for a particularcell 34 in the circuit 30, the controller 42 will open the switch 36 andclose the switch 38 allowing current to travel through the by-pass line40 and around the cell 34. Thus, in this situation, the overall power ofthe circuit 30 or the battery 12 will be decreased by the size of thecell 34 or the percentage of power that the particular cell 34 provided.

The controller 42 can detect a failed, potentially failing and/or lowperforming cell in any manner suitable for the purposes describedherein, many of which are well known to those skilled in the art. Forexample, battery diagnostics currently exist in the art where thevoltage of each battery cell 34 is measured, and compared to a desiredvoltage level to determine cell performance. Further, the temperaturesensors 44 can be used to measure the temperature of each cell 34, or aplurality of cells, to determine whether the temperature of those cells34 exceeds a predetermined maximum temperature threshold indicating ahigh resistance. The actual technique for determining potential cellfailure is unimportant so long as that potential cell failure is able tobe detected and the switches 36 and 38 can be switched accordingly.

Current vehicle technology allows the vehicle control system todetermine that the battery 12 is operating properly and no action needsto be taken, provide a limited battery power mode that provides limitedbattery power in response to a potential battery cell failure mode, andfull battery shut-down where a battery failure has occurred and thesystem disconnects the battery 12 from the vehicle system itself. Thepresent invention provides an additional mode to these three diagnosticmodes where a cell failure or potential cell failure has been detectedand that cell is removed from the series connection of cells so that thebattery 12 can operate normally without that cell.

The embodiment discussed above for the battery circuit 30 includes aby-pass circuit for each battery cell 34. However, depending on thenumber of the cells 34 in the battery 12, providing two switches foreach cell may not be desirable because of insertion losses, componentparasitic losses, etc., associated with each switch. Further, there arevolume and weight considerations that must be addressed as a result ofputting the switches 36 and 38 in the battery enclosure. Further,current battery designs employ specialized circuitry that monitors apredetermined number of the cells for voltage and temperature for aparticular design. However, the more cells that are by-passed during apotential fault condition, the less power the battery 12 is able toproduce because of the loss of the cells. In other words, if a singlecell has failed or is failing and the by-pass circuit by-passes severalcells as a group if one of the cells fails, then all of the powerproduced by those cells is lost even though it is only one cell of thegroup that has a potential problem. Thus, the desirable by-passconfiguration may or may not be to by-pass several cells 34.

FIG. 3 is a schematic diagram of a by-pass circuit 50 showing how aplurality of battery cells 52 can all be by-passed by two switches.Particularly, a first switch 54 is electrically coupled in series withthe plurality of cells 52 and a second switch 56 is provided in aby-pass line 58 around the plurality of cells 52. As above, duringnormal operation, the switch 54 is closed and the switch 56 is open sothat all of the cells 52 are electrically coupled in series in thebattery circuit. If a potential cell problem is detected for any one ofthe plurality of the cells 52, then the switch 54 is opened and theswitch 56 is closed to by-pass all of the cells 52, where the batteryloses the power provided by the group of the cells 52.

The by-pass circuit described above is for series connected batterycells. However, in other battery designs, the battery modules 14 mayeach include a plurality of series connected cells and the modules 14may be electrically connected in parallel. In this configuration, thelowest performing battery module would define the performance of theentire battery as a result of the parallel connection because lowerperforming modules would draw power from higher performing modules.Thus, battery modules with a lower capability would dictate theperformance of the battery regardless of the capability of the higherperforming battery modules.

Different designs could benefit from different electrical configurationsof battery cells by placing some of the cells in series with other cellsand then placing groups of cells that are in series in parallel witheach other. For example, for a modular design having modules of seriesconnected battery cells that can be added to get the desired energy orpower may benefit by electrically coupling standardized series groups ofcells or modules in parallel where adding another cell or module wouldincrease the total power of the battery pack. By electrically couplingadditional battery packs of the same number of battery cells inparallel, the output voltage of the entire battery circuit would remainthe same, but the kilowatt hours of energy the battery would increase bythe number of modules added so that the electrical circuitry used forthe various propulsion motors and other circuits could be the same frombattery circuit to battery circuit.

FIG. 4 is a schematic diagram of a battery pack 60 including parallelconnected strings 62 of series connected battery cells 64, where eachstring 62 includes the same number of cells 64. In this parallelconnected design, the same benefits of a by-pass circuit can be achievedby providing switches at the appropriate locations. As above, eachindividual cell 64 in each string 62 can include its own by-pass circuitwhere if that cell fails, it can be switched out of the particularstring 62. However, a more feasible or cost effective approach may be toswitch the entire string 62 out of the battery pack 60 if one or more ofthe particular cells 64 within that string 62 fails or potentially isfailing. For example, each string 62 may include an electrical device 66at any suitable location along the string 62 where if a potential cellproblem within the string 62 is detected, the device 66 can beelectrically opened to remove that string 62 from the battery packcircuit. Thus, the voltage provided by all of the cells 64 in thatstring 62 will be removed. In this embodiment, the device 66 wouldlikely be a single switch, and can be any of the types of switchesmentioned above, i.e., solid-state switch, relay or mechanicaldisconnect.

As mentioned above, each string 62 may have a varying degreesperformance in its ability to provide a particular state of charge.Those strings 62 that have a lower performance typically draw power fromthe strings 62 that have a higher performance causing the lowerperforming cells or modules to dictate the performance of the batterypack 60. This also applies in the charging mode where weaker cells willdraw disproportionate charging energy and not permit stronger cells tofully charge. Thus, it may be desirable to include a control module asthe device 66, where the module is able to provide cell voltage andstate of charge balancing between the strings 62 that are electricallycoupled in parallel. The module could be designed to also provide anopen circuit so that it also operates as a switch to remove the string62 from the battery circuit, as described above.

FIG. 5 is a schematic diagram of a battery pack parallel interface(BPPI) module 70 that can provide state of charge control in each of thestrings 62 to control the current flow in each string 62. The module 70includes an inputs and logic circuit 72 that controls the operation ofthe module 70. The module 70 also includes two current paths controlledby electronic current regulating devices 74 and 76, such as IGBTs, wherethe direction of current flow during on-off switching modes through eachpath is controlled by the silicon controlled rectifiers (SCR) 78 and 80,respectively. The circuit 72 receives the current signal at the outputof the SCRs 78 and 80. By opening both of the devices 74 and 76, theparticular string 62 will be electrically removed from the battery pack60. The module 70 provides the ability to control current betweenmaximum pack rated and zero current for each individual string 62 thusallowing strings of various capacities and resistances to be connectedin parallel and operated together.

The module 70 coupled to the end of a particular string 62 limits systemperformance based on its capability without degrading the systemperformance of the other strings 62 that may have a higher capability.For example, as the resistance of a particular string 62 changes forwhatever reason, such as deterioration over its life, the switchingcharacteristics of the module 70 causes the string 62 to be switchedinto and out of the circuit at a certain duty cycle. By switching thedevices 74 and 76 in a manner controlled by the circuit 72, the currentflow through the particular string 62 is selectively controlled where itwould be on some percentage of the time and off for some percentage ofthe time.

The battery controller (not shown) would determine the capability ofeach string 62 based on resistance, voltage, temperature, etc., asdiscussed above, and that capability would determine the particularstrings operational limits. Using the state of charge information forall of the strings 62, the controller would determine which string 62had the largest operational range and base the charging and dischargingof the other strings 62 on that range. For example, if the controllerdetermines that one of the strings 62 has 80% of the state of chargerange as the string 62 with the largest state of charge range, then thedevices 74 and 76 would be controlled, depending on whether the batterypack 60 was in a charge or discharge mode, to determine how long thatstring 62 would be switched into the battery circuit. For this example,if the battery pack 60 is in the discharge mode, the circuit 72 wouldopen the device 74 and turn the device 76 on and off at a certain dutycycle that set the amount of time that the string 62 was beingdischarged to be 80% of the total discharge time. Likewise, if thebattery pack 60 is in the charge mode, then the device 76 is open andthe device 74 is turned on and off at a duty cycle that corresponds toit being closed 80% of the charging time. In this manner, theperformance of the battery pack 60 is based on the string 62 having thehighest level of performance and not the lowest performing string 62.

FIG. 6 is a schematic block diagram of a battery circuit 90 includingstrings 92 of series connected battery cells defined herein as groups ofbattery cells 94. Each string includes a BPPI module 96 that operates inthe manner as discussed above. In certain battery pack designs, cellbalancing is required to maintain the voltage of the groups of batterycells 94 to be the same. Thus, the circuit 90 includes cell balancingcircuits 98 for this purpose that operates in a manner well known tothose skilled in the art. The switching characteristics for the devices74 and 76 and the control of the cell balancing circuits 98 aredetermined by a cell balancing controller 100 that provides the signalsfor cell balancing and cell monitoring. A bi-directional inverter andcharge controller 102 sets the amount of charging current for eachstring 92.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

1. A battery circuit comprising a plurality of battery moduleselectrically coupled in parallel, each battery module including aplurality of battery cells electrically coupled in series, each batterymodule also including a control device operable to disconnect thebattery module from the other battery modules in response to batterycell failure or potential failure.
 2. The circuit according to claim 1wherein the control circuit is a switch.
 3. The circuit according toclaim 2 wherein the switch is a solid-state switch.
 4. The circuitaccording to claim 2 wherein the switch is a relay.
 5. The circuitaccording to claim 2 wherein the switch is a mechanical disconnect. 6.The circuit according to claim 1 wherein the control device includescircuit components that control the time that a discharge current flowsfrom the module and a charge current flows to the module.
 7. The circuitaccording to claim 6 wherein the control device includes a logiccircuit, a first current path including a first switch and a secondcurrent path including a second switch, where the first current pathallows current to flow into the module and the second current pathallows current to flow out of the module, and wherein the logic circuitopens the second switch and controls the opening and closing of thefirst switch when the module is being charged where the time that thefirst switch is closed is based on a state of charge range of the modulecompared to the state of charge range of a higher performing module inthe battery circuit, and wherein the logic circuit opens the firstswitch and controls the opening and closing of the second switch whenthe module is being discharged where the time that the second switch isclosed is also based on the state of charge range of the module comparedto the state of charge range of the higher performing module in thebattery circuit.
 8. The circuit according to claim 1 wherein the batterycells are lithium-ion battery cells.
 9. The circuit according to claim 1wherein the battery is a vehicle battery.
 10. The circuit according toclaim 9 wherein the vehicle is a hybrid vehicle.
 11. A battery circuitcomprising a plurality of battery modules electrically coupled inparallel, each battery module including a plurality of battery cellselectrically coupled in series, each battery module also including acontrol device that includes circuit components that control the timethat a discharge current flows from the module and a charge currentflows to the module where the circuit components are operable todisconnect the battery module from the other battery modules.
 12. Thecircuit according to claim 11 wherein the control device includes alogic circuit, a first current path including a first switch and asecond current path including a second switch, where the first currentpath allows current to flow into the module and the second current pathallows current to flow out of the module.
 13. The circuit according toclaim 12 wherein the logic circuit opens the second switch and controlsthe opening and closing of the first switch when the module is beingcharged where the time that the first switch is closed is based on astate of charge range of the module compared to the state of chargerange of a higher performing module in the battery circuit, and whereinthe logic circuit opens the first switch and controls the opening andclosing of the second switch when the module is being discharged wherethe time that the second switch is closed is also based on the state ofcharge range of the module compared to the state of charge range of thehigher performing module in the battery circuit.
 14. The circuitaccording to claim 11 wherein the battery cells are lithium-ion batterycells.
 15. The circuit according to claim 11 wherein the battery is avehicle battery.
 16. The circuit according to claim 15 wherein thevehicle is a hybrid vehicle.
 17. A battery circuit for a battery in ahybrid vehicle, said battery circuit comprising a plurality of batterymodules electrically coupled in parallel, each battery module includinga plurality of battery cells electrically coupled in series, eachbattery module also including a control device that includes circuitcomponents that control the time that a discharge current flows from themodule and a charge current flows to the module where the circuitcomponents are operable to disconnect the battery module from the otherbattery modules, wherein the control device includes a logic circuit, afirst current path including a first switch and a second current pathincluding a second switch, where the first current path allows currentto flow into the module and the second current path allows current toflow out of the module.
 18. The circuit according to claim 17 whereinthe logic circuit opens the second switch and controls the opening andclosing of the first switch when the module is being charged where thetime that the first switch is closed is based on a state of charge rangeof the module compared to the state of charge range of a higherperforming module in the battery circuit, and wherein the logic circuitopens the first switch and controls the opening and closing of thesecond switch when the module is being discharged where the time thatthe second switch is closed is also based on the state of charge rangeof the module compared to the state of charge range of the higherperforming module in the battery circuit.
 19. The circuit according toclaim 17 wherein the battery cells are lithium-ion battery cells.